1. Field of the Invention
The present invention relates to a plasma processing apparatus, and more specifically, to a plasma processing apparatus for preventing unnecessary plasma discharge in the apparatus.
2. Description of the Related Art
Plasma processing apparatuses are used to a CVD apparatus, a dry etching apparatus and the like in a process for manufacturing, for example, an liquid crystal display device. The Plasma processing apparatus will be described below using the CVD apparatus as an example.
Conventional cut-sheet type plasma CVD apparatuses include a chamber for forming a film on the surface of a substance to be processed such as a substrate or the like using a reaction gas introduced into it, a susceptor disposed in the chamber for supporting the substance to be processed and a plurality of susceptor pins accommodated in holes formed to the susceptor.
FIG. 5 is a sectional view showing an example of the susceptor pin used in the conventional plasma CVD apparatus. The susceptor pin 1 is schematically composed of a pin main body 1a, an upper shaft 1b, a lower shaft 1c, and a spring 1d. The core of the pin main body la is composed of aluminum and the periphery of the core is coated with alumina. The upper shaft 1b is a circular cylindrical body composed of hastelloy, and an enlarged diameter section is formed to the upper end of the upper shaft 1b. The lower end of the pin main body 1a is fixed to the enlarged diameter section at the upper end of the upper shaft 1b. The lower shaft 1c is a circular cylindrical body composed of ceramics, an enlarged diameter section is formed to the upper end of the lower shaft 1c, and a recess is formed to the upper surface of the enlarged diameter section. The lower end of the upper shaft 1b is threaded into the hole formed to the bottom surface of the recess formed to the lower shaft 1c and fixed in the hole. The spring 1d is disposed around the upper shaft 1b.
The susceptor pin 1 is accommodated in the hole 3 formed to a susceptor 2. The susceptor 2 is composed of a heating plate 4 for heating the substrate to be heated, a heater 5, and a susceptor shield 6. A gap 7 is defined between the heater 5 and the susceptor shield 6 in view of expansion caused by the heating of the heater 5. A guide 8 is disposed to the inner wall surface of the hole 3 for guiding the rising and falling directions of the susceptor pin.
Next, the operation of the susceptor pin 1 will be described. As shown in FIG. 5, the spring 1d is extended in an ordinary state so that the extreme end of the pin main body 1a is accommodated in the hole 3 of the susceptor 2. When the lower shaft 1c is pushed up from a lower position in the figure, the spring 1d is contracted to thereby project the extreme end of the pin main body 1a from the upper surface of the susceptor 2. When the force for pushing up the lower shaft 1c is released, the spring d returns to its original position and the extreme end of the pin main body 1a is accommodated in the hole 3 of the susceptor 2.
A procedure for forming a film on the surface of the substrate to be processed using the conventional cut-sheet type plasma CVD apparatus will be described.
First, the substrate to be processed is loaded into the chamber by a robot arm or the like in the state that the susceptor pin projects from the upper surface of the susceptor and supported on the susceptor pin. Thereafter, the susceptor pin is accommodated in the hole of the susceptor and the substrate to be processed is placed on the susceptor.
Next, a film is formed on the surface of the substrate to be processed, and after the film is formed, the susceptor pin projects from the upper surface of the susceptor, and the substrate to be processed moves from the susceptor onto the susceptor pin. In this state, the substrate to be processed is unloaded by the robot arm or the like.
When a CVD reaction is performed using the conventional plasma CVD apparatus, since metal components such as the upper shaft 1b, the spring 1d and the like exist in the vicinity of the susceptor pin 1, plasma discharge may arise from these metal components. The inventors have actually confirmed that plasma discharge arises from the lower portion of the susceptor pin toward the bottom surface of the chamber while a CVD job is performed. As a result, there is a problem that a reactant deposited on the susceptor pin causes the defective operation of the susceptor when it rises and falls and the operation failure of the apparatus is caused by the defective operation of the susceptor. Further, there is also caused such problems in the formation of a film that a speed at which the film is formed on the substrate to be processed is lowered, the quality of the film is deteriorated and the in-plane distribution of the film is made uneven. Further, there is a possibility that plasma leaks from the gap 7.
Although the plasma processing apparatus has been described above as to the case that it is used to the CVD apparatus, plasma discharge also arises when the plasma processing apparatus is used to the dry etching apparatus because the susceptor pin has the same structure. Accordingly, there is a possibility that etching cannot be stably performed by the occurrence of the same problem.